import csv
import json
import codecs
from io import BytesIO, StringIO, IOBase
from typing import List, Generator
from pathlib import Path
from dataclasses import dataclass, astuple

import filetype
import pandas as pd
from charset_normalizer import from_bytes

from mindsdb.interfaces.knowledge_base.preprocessing.text_splitter import TextSplitter
from mindsdb.utilities import log

logger = log.getLogger(__name__)

DEFAULT_CHUNK_SIZE = 500
DEFAULT_CHUNK_OVERLAP = 250


class FileProcessingError(Exception): ...


@dataclass(frozen=True, slots=True)
class _SINGLE_PAGE_FORMAT:
    CSV: str = "csv"
    JSON: str = "json"
    TXT: str = "txt"
    PDF: str = "pdf"
    PARQUET: str = "parquet"


SINGLE_PAGE_FORMAT = _SINGLE_PAGE_FORMAT()


@dataclass(frozen=True, slots=True)
class _MULTI_PAGE_FORMAT:
    XLSX: str = "xlsx"


MULTI_PAGE_FORMAT = _MULTI_PAGE_FORMAT()


def decode(file_obj: IOBase) -> StringIO:
    file_obj.seek(0)
    byte_str = file_obj.read()
    # Move it to StringIO
    try:
        # Handle Microsoft's BOM "special" UTF-8 encoding
        if byte_str.startswith(codecs.BOM_UTF8):
            data_str = StringIO(byte_str.decode("utf-8-sig"))
        else:
            file_encoding_meta = from_bytes(
                byte_str[: 32 * 1024],
                steps=32,  # Number of steps/block to extract from my_byte_str
                chunk_size=1024,  # Set block size of each extraction)
                explain=False,
            )
            best_meta = file_encoding_meta.best()
            errors = "strict"
            if best_meta is not None:
                encoding = file_encoding_meta.best().encoding

                try:
                    data_str = StringIO(byte_str.decode(encoding, errors))
                except UnicodeDecodeError:
                    encoding = "utf-8"
                    errors = "replace"

                    data_str = StringIO(byte_str.decode(encoding, errors))
            else:
                encoding = "utf-8"
                errors = "replace"

                data_str = StringIO(byte_str.decode(encoding, errors))
    except Exception as e:
        logger.exception("Error during file decode:")
        raise FileProcessingError("Could not load into string") from e

    return data_str


class FormatDetector:
    supported_formats = astuple(SINGLE_PAGE_FORMAT) + astuple(MULTI_PAGE_FORMAT)
    multipage_formats = astuple(MULTI_PAGE_FORMAT)

    def __init__(
        self,
        path: str | None = None,
        name: str | None = None,
        file: IOBase | None = None,
    ):
        """
        File format detector
        One of these arguments has to be passed: `path` or `file`

        :param path: path to the file
        :param name: name of the file
        :param file: file descriptor (via open(...), of BytesIO(...))
        """
        if path is not None:
            file = open(path, "rb")

        elif file is not None:
            if name is None:
                if hasattr(file, "name"):
                    path = file.name
                else:
                    path = "file"
        else:
            raise FileProcessingError("Wrong arguments: path or file is required")

        if name is None:
            name = Path(path).name

        self.name = name
        self.file_obj = file
        self.format = None

        self.parameters = {}

    def get_format(self) -> str:
        if self.format is not None:
            return self.format

        format = self.get_format_by_name()
        if format is not None:
            if format not in self.supported_formats:
                raise FileProcessingError(f"Not supported format: {format}")

        if format is None and self.file_obj is not None:
            format = self.get_format_by_content()
            self.file_obj.seek(0)

        if format is None:
            raise FileProcessingError(f"Unable to detect format: {self.name}")

        self.format = format
        return format

    def get_format_by_name(self):
        extension = Path(self.name).suffix.strip(".").lower()
        if extension == "tsv":
            extension = "csv"
            self.parameters["delimiter"] = "\t"

        return extension or None

    def get_format_by_content(self):
        if self.is_parquet(self.file_obj):
            return SINGLE_PAGE_FORMAT.PARQUET

        file_type = filetype.guess(self.file_obj)
        if file_type is not None:
            if file_type.mime in {
                "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
                "application/vnd.ms-excel",
            }:
                return MULTI_PAGE_FORMAT.XLSX

            if file_type.mime == "application/pdf":
                return SINGLE_PAGE_FORMAT.PDF

        file_obj = decode(self.file_obj)

        if self.is_json(file_obj):
            return SINGLE_PAGE_FORMAT.JSON

        if self.is_csv(file_obj):
            return SINGLE_PAGE_FORMAT.CSV

    @staticmethod
    def is_json(data_obj: StringIO) -> bool:
        # see if its JSON
        data_obj.seek(0)
        text = data_obj.read(100).strip()
        data_obj.seek(0)
        if len(text) > 0:
            # it looks like a json, then try to parse it
            if text.startswith("{") or text.startswith("["):
                try:
                    json.loads(data_obj.read())
                    return True
                except Exception:
                    return False
        return False

    @classmethod
    def is_csv(cls, data_obj: StringIO) -> bool:
        data_obj.seek(0)
        sample = data_obj.readline()  # trying to get dialect from header
        try:
            data_obj.seek(0)
            csv.Sniffer().sniff(sample)

            # Avoid a false-positive for json files
            if cls.is_json(data_obj):
                return False
            return True
        except Exception:
            return False

    @staticmethod
    def is_parquet(data: IOBase) -> bool:
        # Check first and last 4 bytes equal to PAR1.
        # Refer: https://parquet.apache.org/docs/file-format/
        parquet_sig = b"PAR1"
        data.seek(0, 0)
        start_meta = data.read(4)
        data.seek(-4, 2)
        end_meta = data.read()
        data.seek(0)
        if start_meta == parquet_sig and end_meta == parquet_sig:
            return True
        return False


def format_column_names(df: pd.DataFrame):
    df.columns = [column.strip(" \t") for column in df.columns]
    if len(df.columns) != len(set(df.columns)) or any(len(column_name) == 0 for column_name in df.columns):
        raise FileProcessingError("Each column should have a unique and non-empty name.")


class FileReader(FormatDetector):
    def _get_fnc(self):
        format = self.get_format()
        func = getattr(self, f"read_{format}", None)
        if func is None:
            raise FileProcessingError(f"Unsupported format: {format}")

        if format in astuple(MULTI_PAGE_FORMAT):

            def format_multipage(*args, **kwargs):
                for page_number, df in func(*args, **kwargs):
                    format_column_names(df)
                    yield page_number, df

            return format_multipage

        def format_singlepage(*args, **kwargs) -> pd.DataFrame:
            """Check that the columns have unique not-empty names"""
            df = func(*args, **kwargs)
            format_column_names(df)
            return df

        return format_singlepage

    def get_pages(self, **kwargs) -> List[str]:
        """
        Get list of tables in file
        """
        format = self.get_format()
        if format not in self.multipage_formats:
            # only one table
            return ["main"]

        func = self._get_fnc()
        self.file_obj.seek(0)

        return [name for name, _ in func(self.file_obj, only_names=False, **kwargs)]

    def get_contents(self, **kwargs) -> dict[str, pd.DataFrame]:
        """
        Get all info(pages with content) from file as dict: {tablename, content}
        """
        func = self._get_fnc()
        self.file_obj.seek(0)

        format = self.get_format()
        if format not in self.multipage_formats:
            # only one table
            return {"main": func(self.file_obj, name=self.name, **kwargs)}

        return {name: df for name, df in func(self.file_obj, **kwargs)}

    def get_page_content(self, page_name: str | None = None, **kwargs) -> pd.DataFrame:
        """
        Get content of a single table
        """
        func = self._get_fnc()
        self.file_obj.seek(0)

        format = self.get_format()
        if format not in self.multipage_formats:
            # only one table
            return func(self.file_obj, name=self.name, **kwargs)

        for _, df in func(self.file_obj, name=self.name, page_name=page_name, **kwargs):
            return df

    @staticmethod
    def _get_csv_dialect(buffer, delimiter: str | None = None) -> csv.Dialect | None:
        sample = buffer.readline()  # trying to get dialect from header
        buffer.seek(0)
        try:
            if isinstance(sample, bytes):
                sample = sample.decode()

            if delimiter is not None:
                accepted_csv_delimiters = [delimiter]
            else:
                accepted_csv_delimiters = [",", "\t", ";"]
            try:
                dialect = csv.Sniffer().sniff(sample, delimiters=accepted_csv_delimiters)
                dialect.doublequote = True  # assume that all csvs have " as string escape
            except Exception:
                dialect = csv.reader(sample).dialect
                if dialect.delimiter not in accepted_csv_delimiters:
                    raise FileProcessingError(f"CSV delimeter '{dialect.delimiter}' is not supported")

        except csv.Error:
            dialect = None
        return dialect

    @classmethod
    def read_csv(cls, file_obj: BytesIO, delimiter: str | None = None, **kwargs) -> pd.DataFrame:
        file_obj = decode(file_obj)
        dialect = cls._get_csv_dialect(file_obj, delimiter=delimiter)
        return pd.read_csv(file_obj, sep=dialect.delimiter, index_col=False)

    @staticmethod
    def read_txt(file_obj: BytesIO, name: str | None = None, **kwargs) -> pd.DataFrame:
        # the lib is heavy, so import it only when needed

        file_obj = decode(file_obj)

        text = file_obj.read()

        text_splitter = TextSplitter(chunk_size=DEFAULT_CHUNK_SIZE, chunk_overlap=DEFAULT_CHUNK_OVERLAP)

        docs = text_splitter.split_text(text)
        return pd.DataFrame([{"content": doc, "metadata": {"source_file": name, "file_format": "txt"}} for doc in docs])

    @staticmethod
    def read_pdf(file_obj: BytesIO, name: str | None = None, **kwargs) -> pd.DataFrame:
        # the libs are heavy, so import it only when needed
        import fitz  # pymupdf

        with fitz.open(stream=file_obj.read()) as pdf:  # open pdf
            text = chr(12).join([page.get_text() for page in pdf])

        text_splitter = TextSplitter(chunk_size=DEFAULT_CHUNK_SIZE, chunk_overlap=DEFAULT_CHUNK_OVERLAP)

        split_text = text_splitter.split_text(text)

        return pd.DataFrame(
            {
                "content": split_text,
                "metadata": [{"file_format": "pdf", "source_file": name}] * len(split_text),
            }
        )

    @staticmethod
    def read_json(file_obj: BytesIO, **kwargs) -> pd.DataFrame:
        file_obj = decode(file_obj)
        file_obj.seek(0)
        json_doc = json.loads(file_obj.read())
        return pd.json_normalize(json_doc, max_level=0)

    @staticmethod
    def read_parquet(file_obj: BytesIO, **kwargs) -> pd.DataFrame:
        return pd.read_parquet(file_obj)

    @staticmethod
    def read_xlsx(
        file_obj: BytesIO,
        page_name: str | None = None,
        only_names: bool = False,
        **kwargs,
    ) -> Generator[tuple[str, pd.DataFrame | None], None, None]:
        with pd.ExcelFile(file_obj) as xls:
            if page_name is not None:
                # return specific page
                yield page_name, pd.read_excel(xls, sheet_name=page_name)

            for page_name in xls.sheet_names:
                if only_names:
                    # extract only pages names
                    df = None
                else:
                    df = pd.read_excel(xls, sheet_name=page_name)
                yield page_name, df
